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Eight perennial plant species were selected representing succulent leaved plants, Euphorbia paralias, Zygophylum album, and Gymnocarpos decandrum, shrubs Atriplex halimus, and Lygos raetam, a woody evergreen sub-shrub Ononis vaginalis and the perennial herbs Plantago albicans and Asphodelus microcarpzis. These life-forms characterizing a gradient from non-saline to saline habitats, which are influenced by their distance from the Mediterranean sea coast of northern Egypt. Species were subjected to 500 mM NaCl salinity shock, and significant effects of salinity shock on the metabolic activity in all study species were found. Salinity shock response depended on plant species and it was difficult to find a similar pattern for all species of a specific habitat. An adverse effect of salinity shock was found for E. paralias, O. vaginalis and L. raetam (of sand dune) and G. decandrum, P albicans, and A. microcarpus (of non-saline habitat), which are not exposed to or adapted to salinity stress. The observed regulation of these species to salinity shock resembled that of drought stress. Salinity shock enhanced efficient osmoregulation in some of the study species and disturbed it in the others (mainly the non-saline habitat plants). Malic acid accumulation as a change in the photosynthetic pathway was not inhibited, but its production was inhibited in some species by salinity shock. The variation in water-content of plants did not affect the process of malic acid accumulation. The unfavorable effect of salinity was that it caused a decrease in the protein content of the study species, which decreases their grazing value. (C) 2002 Elsevier Science Ltd.